
where \(G = m G_1 + n G_2\)  is a reciprocal lattice vector of the undistorted monolayer graphene, with integer \(m,n\)  and \(G_1 = \frac{2\pi }{a}(1, -\frac{1}{\sqrt{3}})\)  and \(G_2 = \frac{2\pi }{a}(0, \frac{2}{\sqrt{3}})\) .
The Fourier coefficients \(V_{G}\)  fall off with large \(G\) , so the sum can be truncated after a few shells.
Furthermore, different \(V_{G}\) s are related by symmetries. As a consequence, the adhesion potential has the form [1]}
\(& V[U^-(x)] = c_0 + c_1 \left( \cos (G_1 \cdot U^-) + \cos (G_2 \cdot U^-) \right. \nonumber \\& \left. + \cos ((G_1 + G_2) \cdot U^-) \right) + c_2 \left[ \cos ((G_1 - G_2) \cdot U^-) \right. \nonumber \\& \left. + \cos ((2G_1 + G_2)\cdot U^-) + \cos ((G_1 + 2G_2) \cdot U^-) \right] \nonumber \\& + c_3 \left[ \cos (2G_1 \cdot U^-) + \cos (2G_2 \cdot U^-) \right. \nonumber \\& \left. + \cos (2(G_1 + G_2) \cdot U^-) \right]. \) 
